[LyX/master] Fix dark/light mode setting and run-time switch with Qt 6.8

[Jürgen Spitzmüller]

Am Donnerstag, dem 24.10.2024 um 16:45 +0200 schrieb Yu Jin:
> Not really. What I notice though is that the preferences dialog is
> broken only once, if I close and reopen ist it is better, but still
> not perfect. But the freezes are worse, while LyX is frozen I would
> be able to close and relaunch it like 10 times...

Are you able to do some profiling?

-- 
Jürgen